1. Field of the Invention
The present invention relates to a toner cartridge, an image forming apparatus equipped with the toner cartridge, and an image forming method.
2. Description of the Related Art
A toner cartridge containing a toner for use in printing processing is detachably attached to electrophotographic image forming apparatuses such as a laser printer, a copying machine and a multifunctional peripheral. When printing processing is performed in the image forming apparatus, a toner in the toner cartridge is gradually consumed. When the cartridge becomes empty, the used and empty cartridge is exchanged for a toner cartridge having a toner filled therein.
The cartridge is a rectangular parallelepiped in appearance, and comprises a container body having a toner containing space for containing a toner, and a toner conveying screw provided in the container body. The toner conveying screw is provided with a spiral toner conveying blade on a rotation shaft extending in parallel in a longitudinal direction of the container body, and conveys the toner in the container body toward a toner discharge port by rotating the rotation shaft about an axis thereof. The toner conveyed is discharged from the toner discharge port toward a developing device.
The toner conveying screw is provided so as to have a clearance to an inner wall surface of the container body. When the clearance is set to be small, toner conveying capability by the toner conveying screw can be improved.
However, in the cartridge in which the clearance is set small, when the toner conveying screw rotates, friction force imparted to a toner entered the clearance is increased, and as a result, toner aggregation occurs in the state that toner particles are packed with each other. The toner aggregated in the packed state decreases chargeability, and this gives rise to the problem that the toner is not charged in an appropriate charged amount in a developing device, resulting in deterioration of quality of an image printed.
To overcome such a problem, Japanese Unexamined Patent Publication JP-A 2004-334054 discloses a toner cartridge having a toner conveying screw, in which an outer diameter of a spiral blade is formed locally small, a period of the spiral (pitch) of the spiral blade is set small, or an outer diameter of a spiral blade is formed locally small and a period of the spiral (pitch) of the spiral blade is set small. According to the toner cartridge disclosed in JP-A 2004-334054, the friction force imparted to a toner entered a clearance between the toner conveying screw and an inner wall surface of a container body is reduced by locally reducing conveying capability of the toner conveying screw, thereby occurrence of toner aggregation can be inhibited.
However, in the toner cartridge disclosed in JP-A 2004-334054, even though occurrence of toner aggregation can be inhibited, toner conveying capability by the toner conveying screw is decreased, resulting in decrease in toner replenishing capability to a developing device.